Human blood vessels often become occluded or completely blocked by plaque, thrombi, other deposits, emboli or other substances, which reduce the blood carrying capacity of the vessel. Should the blockage occur at a critical place in the circulatory system, serious and permanent injury, or even death, can occur. To prevent this, some form of medical intervention is usually performed when significant occlusion is detected.
A serious example of vascular occlusion is coronary heart disease, which is a common disorder in developed countries and is the leading cause of death in the United States. Damage to or malfunction of the heart is caused by narrowing or blockage of the coronary arteries that supply blood to the heart. The coronary arteries are first narrowed and may eventually be completely blocked by plaque (atherosclerosis), and the condition may further be complicated by the formation of thrombi (blood clots) on roughened surfaces of, or in eddy currents caused by the plaques. Myocardial infarction can result from atherosclerosis, especially from an occlusive or near-occlusive thrombus overlying or adjacent to the atherosclerotic plaque, leading to ischemia and/or death of portions of the heart muscle. Thrombi and other particulates also can break away from arterial stenoses, and this debris can migrate downstream to cause distal embolization.
Various types of intervention techniques have been developed to facilitate the reduction or removal of a blockage in a blood vessel, allowing increased blood flow through the vessel. One technique for treating stenosis or occlusion of a blood vessel is balloon angioplasty wherein a balloon catheter is inserted into the narrowed or blocked area, and the balloon is inflated to expand the constricted area. Other types of interventions include atherectomy, deployment of stents, local infusion of specific medication, and bypass surgery. Each of these methods is not without the risk of embolism caused by the dislodgement of the blocking material, which may then move downstream.
Often, more than one interventional catheter is used during a procedure, such as to change the size of the balloon being used or to introduce additional devices into the system to aid with the procedure, including stent delivery catheters and aspiration catheters. In such situations, the catheters are generally inserted into the patient's cardiovascular system with the assistance of a guidewire. For example, a guidewire is introduced into the patient, steered through the tortuous pathways of the cardiovascular system, and positioned across an intended treatment location. Various catheters having a lumen adapted to receive the guidewire may then be introduced into and removed from the patient along the guidewire, thereby decreasing the time needed to complete a procedure.
Many techniques exist for preventing the release of thrombotic or embolic particles into the bloodstream during such a procedure. Common among these techniques is introduction of an occlusive device or a filter downstream of the treatment area to capture these embolic or thrombotic particles. The particles may then be removed from the vessel with the withdrawal of the occlusive or filtering device. In another common technique, the particles may be removed by an aspiration catheter prior to the withdrawal of these devices. Aspiration catheters have also been found useful in removing thrombus prior to crossing underlying atherosclerotic plaque with guidewires and/or treatment catheters. Such preliminary removal of thrombus makes it easier to cross the stenosis and less likely to release thromboembolic particles into the bloodstream during the procedure.
An aspiration catheter may be designed such that a guidewire is contained within the aspiration lumen as the catheter is advanced there over, or the aspiration catheter may include a dedicated guidewire lumen extending along substantially the entire length of the aspiration catheter such that the guidewire is disposed therein as the catheter is advanced through a body lumen. Such dual-lumen catheters having an aspiration lumen and a guidewire lumen may be constructed in a variety of ways including relatively simple profile extrusions, more complex assemblies of different tubular components, and combinations of these two methods.
Dual-lumen profile extrusions can have parallel round lumens surrounded by relatively uniform walls, resulting in a non-circular, generally figure-eight shaped transverse cross section. Alternatively, if a circular outer profile is desired, then dual-lumen profile extrusions can have parallel round lumens with non-uniform wall thicknesses or various other combinations of lumens having unequal sizes and non-round shapes such as D-shapes or crescent-shapes, as will be understood by those of skill in the field of cardiovascular catheters.
One of the important features of aspiration catheters is the ability to rapidly and efficiently aspirate even large embolic particles without the need to first break them into smaller sub-particles. This advantage is achieved, at least in part, by providing the catheter with an aspiration lumen having as large a cross sectional area as possible, given overall size constraints of the catheter design. In embodiments having an aspiration lumen that is crescent shaped or has another non-round shape, a relatively large cross-sectional area is preferably maintained to achieve rapid and efficient aspiration.
Aspiration catheters may also be of the single operator type. A single operator aspiration catheter typically includes a tubular catheter shaft with an aspiration lumen extending the entire length thereof and a substantially shorter guidewire lumen extending along a distal portion of the catheter. As such, the guidewire is located outside of the aspiration catheter except for a short guidewire segment that extends within the guidewire lumen. Advantageously, a clinician is able to control both ends of the guidewire while the aspiration catheter is loaded or exchanged onto the guidewire, which may be already indwelling in the patient. The aspiration catheter is then advanced through the patient's vasculature with only a distal portion of the catheter riding on the guidewire.
Several types of aspiration catheters are disclosed in U.S. Patent Application Publication No. 2002/0177800, which is incorporated by reference herein in its entirety. One of the aspiration catheters in the '800 publication comprises a first elongate flexible tube having a proximal end and a distal end. The first tube incorporates reinforcement such as a metallic braid or coil or a polymer coil to provide strength and flexibility to the device. An aspiration lumen extends the length of the first tube, and an aspiration port at the proximal end of the first tube is in fluid communication with the aspiration lumen, such that partial vacuum for aspiration can be provided through the port and aspiration lumen. A second tube is disposed alongside the first tube and has a lumen adapted to receive a guidewire there through. The second tube can extend substantially the entire length of the first tube, or can extend less than 40 cm in a proximal direction from the distal end of the first tube.
In comparison to dual-lumen extruded catheters, the exemplary aspiration catheter of the '800 publication is assembled from several different components, each of which can be varied or selected to provide desirable features. For example, the disclosed reinforcement may comprise a braid having a varying pitch to advantageously change the flexibility along the length of the aspiration catheter. Alternatively, or in addition, the flexibility of the catheter can be varied by using different polymers to make different portions of the catheter.
As is well known by those skilled in the field of interventional catheterization, guiding catheters are often used when a treatment site is remote from a percutaneous entry point into the patient. Guiding catheters greatly facilitate the navigation or exchange of various devices during a procedure, although their use creates a slightly larger puncture site. It is advantageous to use a guiding catheter with a small outside diameter in a vascular intervention because the time required to close the puncture site is directly related to the diameter of the guiding catheter. Extensive product development has already provided state-of-the-art guiding catheters with very thin walls. Thus, further down-sizing of guiding catheters requires down-sizing of the entire catheter system. That is, guiding catheters having smaller outside diameters also have smaller inside diameters that can only receive interventional devices with concomitantly reduced diameters or transverse outside dimensions.
While the exemplary aspiration catheter of the '800 publication offers numerous performance advantages such as good handling and aspiration efficiency, the catheter is somewhat inefficient in its use of cross-sectional space. To fit the exemplary aspiration catheter of the '800 publication through ever-smaller guiding catheters requires significantly compromising the size of the aspiration lumen in particular, thus reducing the aspiration efficiency of the catheter. There is therefore a need for an improved aspiration catheter that offers an opportunity for reducing the size of the overall interventional catheterization system without diminishing the above stated performance merits of the aspiration catheter.